Conventionally, a system including a particulate collection filter (DPF: diesel particulate filter) composed of a porous ceramic has been known for collecting C (carbon)-based particulates (PM) exhausted from a diesel engine. PM is gradually deposited on a DPF through continuous use of a diesel engine. PM deposited on a DPF is combusted at an appropriate timing to be oxidized and removed, so as to prevent cracking of the DPF or the like or leakage of the PM toward a downstream side of the DPF. Additionally, if regeneration of a DPF is conducted before a certain amount of PM is deposited on the DPF, degradation of fuel consumption is caused. Therefore, a DPF with PM deposited thereon is regenerated at an appropriate timing.
In order to measure an amount of PM deposited on a DPF to provide an appropriate timing of combustion of such PM, it is considered that a pressure sensor is provided on each of an upstream side exhaust gas flow path and a downstream side exhaust gas flow path for the DPF and each of a ratio of magnitudes of alternating current components of outputs of respective pressure sensors and a difference between direct current components thereof is calculated (for example, see Patent Document 1).